Aside from all of the excellent points made here by fellow Catholics - and they are excellent - I’d like to mention one more thing in light of the Theology of the Body.
It is very true many people do not understand what marriage is. Our Holy Father Pope St. John Paul II started by looking at what Christ said about marriage.
Consider the bolded parts. Yes, it is true this is about divorce. But divorce is only one of many compromises to marriage. And note that Jesus focuses less on the fact of divorce than on the nature of marriage. He says “In the beginning…”. Our Lord is appealing to the “beginning” of human nature.
Do you remember the first creation story in Genesis? How it ended?
“Let us make man in our image, after our likeness”. Consider, then, the events of the first creation story in light of this astounding fact: that, whatever we be as humans, He made us in His image. Read the Creation stories in Genesis 1 and 2 again, in light of that. Does it tell you anything?
**Pope John Paul II had this revelation, briefly: that God’s life, in the Trinity, between Father, Son and Holy Spirit, is quite like the relationship between man and woman and child. In the Catholic Church, the Creed says the Holy Spirit “proceeds from the Father and the Son”. Consider how children come into the world. Is it not a co-operation of man and woman that causes children to be created - even in IVF or artificial insemination? **
So the coital act, the marital act, the conjugal act, is an act 1) of creativity, just as God’s love created the entire universe, and 2) of unity, just as that creative love unites the Father, Son, and Holy Ghost in one nature - love.